The community was named after James Buchanan, the 15th President of the United States.[7] Popularly known as "Redbud City" because of the many redbud trees that have historically lined city streets and the major approaches to the city, Buchanan has long been recognized as a Tree City USA by the National Arbor Day Foundation.

The St. Joseph River was once a major transportation route for Native American tribes in the area, especially the Potawatomi, and a historical marker to that effect has been placed on Moccasin Trail north of Buchanan near Batchelors Island.[8]

As of the census[3] of 2010, there were 4,456 people, 1,901 households, and 1,136 families residing in the city. The population density was 1,782.4 inhabitants per square mile (688.2/km2). There were 2,139 housing units at an average density of 855.6 per square mile (330.3/km2). The racial makeup of the city was 86.6% White, 7.5% African American, 1.2% Native American, 0.3% Asian, 1.3% from other races, and 3.1% from two or more races. Hispanic or Latino of any race were 3.3% of the population.

There were 1,901 households of which 31.5% had children under the age of 18 living with them, 40.1% were married couples living together, 13.3% had a female householder with no husband present, 6.4% had a male householder with no wife present, and 40.2% were non-families. 34.8% of all households were made up of individuals and 14.9% had someone living alone who was 65 years of age or older. The average household size was 2.34 and the average family size was 3.01.

The median age in the city was 37.6 years. 24.6% of residents were under the age of 18; 9.3% were between the ages of 18 and 24; 26.3% were from 25 to 44; 25.6% were from 45 to 64; and 14.3% were 65 years of age or older. The gender makeup of the city was 48.1% male and 51.9% female.

There were 1,915 households out of which 30.9% had children under the age of 18 living with them, 44.5% were married couples living together, 13.3% had a female householder with no husband present, and 37.8% were non-families. 32.0% of all households were made up of individuals and 14.7% had someone living alone who was 65 years of age or older. The average household size was 2.41 and the average family size was 3.05.

The age structure of the population was diffuse, with 25.6% under the age of 18, 9.6% aged 18–24, 29.0% aged 25–44, 21.3% aged 45–64, and 14.5% 65 years of age or older. The median age was 35. Sex ratio was skewed toward females, with 87.5 males for every 100 females of all ages and 83.1 males for every 100 females 18 years or older.

Median income was $34,244 for a household and $43,860 for a family. Males had a median income of $32,950 versus $21,857 for females. Per capita income was $16,600. About 10.9% of families and 12.4% of the population were below the poverty line, including 14.7% of those younger than 18 and 10.7% of those older than 64.

Buchanan was historically known as the headquarters for Clark Equipment Company, a manufacturer of truck axles, fork lift trucks, front-end loaders, and other heavy machinery. The company was formed in 1916 out of an acquisition of two other Buchanan companies.[13] Clark left the area in the 1990s, forcing the city to diversify, and a number of smaller businesses took over the buildings Clark essentially donated to the city.

Electro-Voice, a manufacturer of high quality audio equipment such as microphones, amplifiers and loudspeakers, was also headquartered in Buchanan.

Pears Mill, a flour mill using the water power of the swiftly flowing McCoy Creek, was built in 1857 and still stands. It is open during the summer for visitors.

The Tin Shop Theatre, located near Pears Mill, is a small theater with performances in the summer. The seasons run into September and a variety of shows for everyone of any age and any occasion are performed there.

The Redbud MX motocross track, part of the AMA National Motocross, sits in Buchanan. It is home to the biggest jump in the circuit, "Larocco's Leap." Named after 250cc and 500cc Motocross Champion Mike Larocco. Every Fourth of July, Redbud MX hosts a professional AMA motocross race in Buchanan. The track holds professional Traxxas TORC Series off road buggy and truck races and it has held off-road races in the SODA days.

Buchanan consists of two elementary schools, Ottawa, and Moccasin (grades K-4), with Ottawa and Moccasin making up most of the elementary age students. Stark Elementary was closed after the 2010-2011 school year due to low budget of the school. Buchanan also features one middle school (grades 5-7) and Buchanan High School, currently a Class B school in terms of student population (and, therefore, athletic participation). Known as the Bucks, BHS has a strong reputation for success in high school sports, namely their Men's tennis program, which qualified for the MHSAA state championship every year for 17 years, the last being 2009. They were state champions in basketball in 1976 and 1978, baseball in 1985, Women's Basketball in 1990, Men's Track & Field in 1999, and tennis in 2003.

Buchanan is located 1.5 miles (2.4 km) north of US 12, 2.3 miles (3.7 km) west of US 31, 9.3 miles (15.0 km) north of the US 31 interchange on the Indiana Toll Road (I-80|I-90), and 20 miles (32.2 km) east of I-94 (exit 4 via US 12).